There are about 70 cases of American parents who are kept from seeing their children in Japan, and U.S. Assistant Secretary of State Kurt Campbell met with several of them in a group earlier Tuesday. He called their situations “heart-breaking.”

In some cases, Japanese mothers living overseas have fled to Japan with their children and kept the fathers from having any contact with the kids, even if court rulings abroad ordered joint custody.

“This situation has to be resolved in order to ensure that U.S.-Japan relations continue on such a positive course,” Campbell told reporters in Tokyo. “The United States government strongly believes that these children have a right to enjoy the love of both parents and the benefits of both cultures.”

Campbell’s comments are the strongest to date on this issue, with Tokyo coming under increased international pressure to sign on to the Hague Convention on International Child Abduction, which is designed to address such international custody disputes.